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Universe Luminosity Function and CBR energy density evolution?



 
 
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  #1  
Old November 23rd 16, 07:45 PM posted to sci.astro.research
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Default Universe Luminosity Function and CBR energy density evolution?

Does anyone know of a good paper showing the luminosity of the
universe as a function of age of the universe? ie, a plot showing
total L per unit co moving volume, for each Gyr time back to early
universe.

Also, I'm trying to figure out how to account for the change in
energy per m^3 of space, for the cosmic background radiation, as a
function of age of the universe. As we go back in time, the CBR
would have been at higher energy, so, the CBR energy per m^3 would
have been higher in the early universe than it is today.

Maybe a web site that talks about these aspects of cosmological
evolution?

Thanks,

rt
  #2  
Old November 24th 16, 07:37 AM posted to sci.astro.research
Phillip Helbig (undress to reply)[_2_]
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Default Universe Luminosity Function and CBR energy density evolution?

In article ,
writes:

Does anyone know of a good paper showing the luminosity of the
universe as a function of age of the universe? ie, a plot showing
total L per unit co moving volume, for each Gyr time back to early
universe.


Look up "Madau diagram". This isn't exactly what you want, but might
point you in the right direction.

It also depends on what you mean by "luminosity". To a first
approximation, all photons are CMB photons. Hoyle pointed out that the
total amount of energy emitted by stars in the last few billion years is
about the same as that of the CMB. (He thought that this might indicate
that the CMB is recycled starlight---of course, he didn't believe in the
Big Bang---and was looking for an alternative explanation for the CMB.)

Check out papers from the late 1970s by the late Paul Wesson and (still
alive, as far as I know---saw him last year) Rolf Stabell on
extragalactic background light.

Also, I'm trying to figure out how to account for the change in
energy per m^3 of space, for the cosmic background radiation, as a
function of age of the universe. As we go back in time, the CBR
would have been at higher energy, so, the CBR energy per m^3 would
have been higher in the early universe than it is today.


This is easy: radiation density is proportional to the fourth power of
(1+z), where z is the redshift. Three powers of (1+z) come from the
expansion, and the fourth comes from the fact that the wavelength
stretches with the expansion of the universe. Black-body radiation
remains black-body radiation when stretched this way, the temperature
being proportional to (1+z).
  #3  
Old December 11th 16, 06:30 AM posted to sci.astro.research
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Default Universe Luminosity Function and CBR energy density evolution?

On Wednesday, November 23, 2016 at 10:37:33 PM UTC-8, Phillip Helbig (undress to reply) wrote:
This is easy: radiation density is proportional to the fourth power of
(1+z), where z is the redshift. Three powers of (1+z) come from the
expansion, and the fourth comes from the fact that the wavelength
stretches with the expansion of the universe. Black-body radiation
remains black-body radiation when stretched this way, the temperature
being proportional to (1+z).


Rho_E is energy density for cbr.

So, you're saying Rho_E_today * (1 + 1)^4 = 16 Rho_E_today

is equal to the cbr energy density at redshift z = 1.

So, the energy density today is 1/16 th of the energy density back then.

(Did I get this right?)

Thanks,

rt

[[Mod. note -- That's correct. -- jt]]
  #4  
Old December 12th 16, 04:39 AM posted to sci.astro.research
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Default Universe Luminosity Function and CBR energy density evolution?

On Saturday, December 10, 2016 at 9:30:36 PM UTC-8, wrote:
On Wednesday, November 23, 2016 at 10:37:33 PM UTC-8, Phillip Helbig (undress to reply) wrote:
This is easy: radiation density is proportional to the fourth power of
(1+z), where z is the redshift.


Further checking.....

So, at recombination, z ~= 1100 the energy density was around.....

Rho_E ~ 4000 K ~ 4.005E-14 (1+ 1100)^4 = 0.059 J/m^3

Still make sense?

I'm not sure what the equation is to relate a thermal temperature to an energy density to check if that energy density matches that temperature.

Thanks,

rt

[[Mod. note -- A handy compendium of forumulas for black-body radiation
(including the cosmic microwave background) is
http://hyperphysics.phy-astr.gsu.edu...m/raddens.html
The answer to your last question is the last formula on that webpage.
-- jt]]
  #5  
Old December 12th 16, 10:02 PM posted to sci.astro.research
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Default Universe Luminosity Function and CBR energy density evolution?

So, you're saying Rho_E_today * (1 + 1)^4 = 16 Rho_E_today

is equal to the cbr energy density at redshift z = 1.

So, the energy density today is 1/16 th of the energy density back then.



[[Mod. note -- That's correct. -- jt]]


So, I found a value for CBR energy density today on Wiki at 4.005E-14
J/m^3. Using multiplier of (1 + z)^4, I get the following values for
lookback times in 1 Gyr increments. z values came from Ned Wright's
calculator using default settings.

I'm pretty sure I did the math right, but, do the values for CBR energy
density sound about right?

z J/m^3
0 4.005E-14
0.075 5.34855E-14
0.15885 7.2229E-14
0.2534 9.88465E-14
0.3616 1.37658E-13
0.4873 1.95973E-13
0.6363 2.87114E-13
0.8178 4.37307E-13
1.0462 7.02093E-13
1.3474 1.21605E-12
1.7715 2.36299E-12
2.434 5.56934E-12
3.677 1.91634E-11
7.368 1.96376E-10

 




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